Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $237.79   3.453%   $246.0009   $246.00   $246.00   $246.00  
  Purchase #2 $136.67   10.465%   $150.9725   $150.97   $150.95   $151.00  
  Purchase #3 $214.25   5.378%   $225.7724   $225.77   $225.75   $225.80  
  Purchase #4 $76.37   9.379%   $83.5327   $83.53   $83.55   $83.50  
  Purchase #5 $216.39   9.192%   $236.2806   $236.28   $236.30   $236.30  
  Purchase #6 $98.95   11.700%   $110.5272   $110.53   $110.55   $110.50  
  Purchase #7 $201.79   9.649%   $221.2607   $221.26   $221.25   $221.30  
  7 purchase totals = $1,182.21       $1,274.3470   $1,274.34   $1,274.35   $1,274.40